A typical connection box for a solar panel or module has a base that is attached to the solar module, in particular glued to the solar module and forming a cavity for various function parts and for electric cables and their contacts, and having a cover that closes off the cavity of the base from the environment. The connection box has a strain relief device for a cable entering into the connection box, formed in particular by an aperture or partial opening on the cover side and on the bottom side, together forming a cable hole that forms the strain relief device and is manufactured to be undersized in comparison with the cable so that it grips it tightly.
Connection boxes for solar modules are usually mounted on the back of the modules, in particular glued there. They serve to electrically connect the solar modules to a composite network. To do so, the film conductors, usually in the form of ribbon cables coming out of the solar module, are connected to single-pole round cables inside the connection box. In addition, the connection box serves to receive various function elements, for example, bypass diodes.
High demands are made of the stability and imperviousness of connection boxes for solar modules. The lifetime of such a connection box must correspond at least to the average lifetime of a solar module of 25 years with full functionality. For this reason, connection boxes for solar modules are made of high-grade plastic and accurately fitted components that are sealed with respect to one another in a complex manner. The interior is completely sealed off from the outside. To prevent condensate in the connection box, gas vents by which the interior is connected to the exterior environment are usually provided.
The strain relief of the conductors entering the connection box is especially important. In the prior art, these are usually operated by cap nuts that hold the cable via crimp tongues. These have the significant disadvantage that the cable must be inserted through a hole into the connection box in a very tedious manner, which significantly impedes machine preassembly of the connection box and its preassembly with cables entering the connection box. It is also known that the incoming cables may be provided with crimp sleeves that are supported on suitable components within the connection box in a stress-relieving manner.
DE 20 2008 006 119 discloses a strain relief designed for the applicant's connection box having an especially simple design but a satisfactory effect in all regards. In this case the cable is guided inside the connection box at a 45° angle. The entrance opening for the cable is formed by two complementary apertures in the base and the cover part. The important advantage of this connection box may be seen in the fact that the cable can be inserted into the base of the connection box and need not be pushed through a hole, so that machine preassembly is easily implementable. In addition, the strain relief based essentially only on the angled cable guide is technically extremely simple but is achieved in a highly effective manner. The apertures that form the entrance opening for the cable in the case of an installed cover, are manufactured to be slightly undersized relative to the cable so as to seal around and grip the cable.
However, in practice it has been found that additional strain relief for the connection box is advantageous in particular with respect to tension in the cable directed at an angle toward the fastening surface of the connection box on the solar module because these forces also act against the closing forces of the connection box.